The COA (Color-filter on Array) technology is an integration technology that fabricates a color filter layer on an array substrate directly, which can effectively avoid the problem of light leakage of a liquid crystal display device in a box-aligning process due to an alignment deviation, and can also improve the display opening ratio significantly.
The structure of a conventional array substrate of the COA technology is shown in FIG. 1, wherein the structure comprises a substrate 101, a gate line layer (including a gate line, a gate 102, and a common electrode), a gate insulating layer 103, a semiconductor layer 104, a data line layer (including a data line, a source 105, and a drain 106), an insulating layer 107, a color filter layer 108, a light shielding layer 109, and a pixel electrode 110. The material of the color filter layer 108 is a color photoresist. A common electrode (not shown) is located under the color filter layer 108 and is opposite to the pixel electrode 110 so as to form a storage capacitance. The pixel electrode 110 is electrically connected with the drain 106 through a via hole.
The size of the capacitance is inversely proportional to the spacing between two polar plates that form the capacitance, and the color filter layer 108 generally requires a relatively great thickness. Therefore, in the prior art, the spacing between the pixel electrode 110 and the common electrode of the array substrate integrated with the color filter layer 108 is relatively large, which results in a relatively low storage capacitance that cannot meet the requirement of leakage current in the display cycle. Consequently, the display stability is reduced.
Moreover, since the via hole for electrically connecting the pixel electrode 110 and the drain 106 needs to pass through the thick color filter layer 108, the depth of the via hole is extremely large, such that it is difficult to control the shape of the via hole, and it is easy to result in an excessive aperture ratio of the via hole, thereby causing the opening ratio of the pixel to be reduced. Additionally, if the gradient angle of the inner wall of the relatively deep via hole is too abrupt, breakage of the pixel electrode 110 carried thereon may result, thereby reducing the display quality.